If you place a copy of the field on your layout and remove the radio button formatting, you'll see the "other" values. You can place this field next to the radio button formatted copy and use conditional formatting to hide the contents of the field if the selected value is a member of the radio button value list.
The expression could be: ValueCount ( FilterValues ( ValueListItems ( get ( FileName ) ; "ValueListNameInQuotes" ) ; table::radiobuttonfield ) )
and then select a font size of 500 as the format so that the value is not visible if it's selected from one of the existing radio button values.
Thank you, again!